Ocular physiology_2014

1Subrata RoyProduct Executive, PMD

+88-01713-374737

EYE

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• Eye is the sensory organ which helps us to vision.

• Eye ball is nearly spherical structure with a diameter of approximately 22 to 27 mm.

The orbit is the bony hollow region of skull that contains the eyeball.

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Orbit

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Contents of Eyeball

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Eye Lashes & Eyebrows

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The eye lids are two movable folds situated above and below the front of the eye.

Composition (Eyelids):• Skin-The thinnest part of

human body• Muscle-Open & close the

eyelid• Connective tissue-Give

rigidity & support• Conjunctiva-the mucous

membrane acting as a lubricating film between the eyelid & sclera

Eyelid

The Blinking of the eyelids helps to spread the tears evenly over the eye and by renewing the tear film as it evaporates, prevents the eye drying out.

Normal blinking occurs about 12 times per minute.

During each blink, Our eyes are shut for around 0.3 seconds

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Blinking

EYE MUSCLE

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The eye is spherical hollow, the periphery

of which composed of the three major layer or coats

1. Outer Fibrous Layer (Cornea-

Sclera) 2. Middle Vascularized Layer (Uvea:

Choroid-iris-ciliary body)

3. Inner Neural layer(Retina)

Outer Fibrous layer

Middle Vascular Layer

Inner Neural Layer 10

CONJUNCTIVA

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Thin, transparent mucous membrane lining posterior surfaces of eyelids and covering anterior surface of the eyeball, excluding cornea

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What are the parts of the conjunctiva?Clinically, the conjunctiva divided into three parts: •The Palpebral (Latin word “palpebrae” means “an eyelid) -- which lines the under-surface of the eyelids, •The Bulbar -- which coats the anterior portion of the sclera except cornea.•The Fornix – Conjunctival junction between the The Palpebral and The Bulbar conjuntiva

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Contains goblet cells which secrete lubricating mucus and helps keep they eyeballs moist

It also helps the sclera protect the eye.Protects the inside of eye from infection

and damage from foreign bodies

Function of Conjunctiva

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Cornea – "window of the eye“

(Outer Layer)

Transparent structure forming the front portion of eye. The average adult cornea is 1.0 mm thick and 11.5 mm in diameterThe cornea is avascular (contains no blood vessels). Its nutritional and metabolic needs are met by:

blood vessels supplying the  (the junction of the sclera and cornea)fluids that make up the precorneal tear film components of the tear film aqueous oxygen from the external environment

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Layers of cornea

Function: Provide the principal refracting medium for the eye

The cornea has five main layers of cells:1. Epithelium: The outer layer of the cells that acts as a barrier against damage and infection2. Bowman's membrane: A thin, tough membrane3. Stroma: Consist of collagen fibers and account for 90% of the cornea's thickness4. Descemet's membrane: A thin membrane of collagen and elastic fiber5. Endothelium: A layer very delicate cells that cannot regenerate and are Responsible for maintaining partial corneal dehydration and transparency

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Sclera:The tough white outer coat of the eyeballwhite outer coat of the eyeball, continuous with cornea. The sclera is completely opaque, preventing light from entering the eye .•Function: Forms the shape & maintain the shape of the eyeball

Sclera – "white of the eye“

(Outer Layer)

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The iris, ciliary body, and the choroid are all continuous with each other and are collectively called the uvea.

UVEA/Uveal Tract(Middle Vascular Layer)

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•The iris, which is the colored part of the eye, contracts and dilates to control how much light enters the eye. •It is made up of smooth muscle fibers that adjust pupil size .•By adjusting, it allows us to see under a variety of lighting conditions.

Iris(Middle Layer)

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PupilThe pupil is a black hole in the centre of the iris. The size of the pupil determines the amount of light that enters the eye. The pupil size is controlled by the dilator and sphincter muscles of the iris.

•Pupil diameter :In healthy eye, ranges from 2 to 8 millimeters.

If you are in a very bright room, or in bright sunlight, our pupils will be very small. This is because not much light needs to be let in to the eye for it to be able to see well. In a dimly-lit room your pupils will be bigger, to let as much light into the eye as possible.

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Function of iris and pupil

• Regulate the amount of light entering the eye

The choroid is a layer of connective tissue and blood vessels, located between the sclera (white of the eye) and the retina.

Function: Provides nourishment to surrounding eye structure

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Choroid (Middle Layer)

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The ciliary body releases aqueous humor, which nourishes the front part of the eye. It also contains the ciliary muscle, which changes the shape of the lens to help you focus.The ciliary body is made up of:•ciliary processes•ciliary muscles•Zonules

The ciliary body (Middle Layer):

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AQUEOUS HUMOR

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• Aqueous humor is the fluid contained in the eye between the lens and cornea.•This fluid is produced by the ciliary body and drains through the trabecular meshwork. Function: •nourishes & baths cornea, iris and lens and maintain intraocular pressure •It carries the nutritional elements needed for the avascular cornea and lens.

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Ciliary body Produces aqueous

humorfilling the posterior chamber (space between the iris and the

lens.)

outwards into the angle(formed by the iris and cornea. )

flows through the pupil into the anterior chamber

(between the cornea and the iris.)

Filtering through the trabecular meshwork

Pass through Canal of Schlemm

returns back into the blood circulation.

Ciliary body Drainage system

CANAL OF SCHLEMM

The canal of schlemm provides a route for excess aqueous humor to drain out of the eye. Canal transfers approximately 2-3 micro liters of aqueous humor/minute

Function : It lies near the junction of cornea and sclera, this canal passes circularly around the cornea, and drains the aqueous humor.

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CRYSTALLINE LENS

The crystalline lens is a biconvex, transparent & avascular structure. It is located immediately behind the iris.

Suspended by fine ligament (Zonules), attached between ciliary process

completely transparent structure about 4 mm thick and 9 mm in diameter.

Function: Focuses image on the retina

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Lens can be divided into three regions

1. Capsule2. The anterior epithelium/lens

cortex3. The lens fibre / lens nucleus.

CHAMBER OF THE EYE

There are actually three chambers in the eye.

The anterior chamber The posterior chamber The vitreous chamber

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The cavity in the front part of the eye between the iris and cornea is called the Anterior Chamber.

It is filled with Aqueous, a water-like fluid. This fluid is produced by the ciliary process.

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Anterior Chamber

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The posterior chamber is the fluid-filled space immediately behind the iris but in front of the lens.

Posterior chamber

VITREOUS CAVITY /VITREOUS CHAMBER

The vitreous cavity fills the space from the lens to the retina and contains vitreous humor, a jelly-like material that maintains internal pressure to support the eyeball and transports nutrients to the cornea.

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VITREOUS HUMOR

The vitreous humor is a clear, transparent gel of semisolid consistency which fills the chamber between the posterior surface of the lens and the inner surface of the retina. It is 99% water, with the remainder being mostly a viscous substance called hyaluronic acid. It occupies two-thirds of the volume of the globe (eyeball)

Function: 1. Provide physical support Function: 1. Provide physical support 2. Transmit light to retina 2. Transmit light to retina

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The retina is a very thin layer of tissue that lines the inner part of the eye.  It is connected to the brain.Function: Received and transmit visual input

Retina(Innermost Neural Layer)

The retina contains photoreceptor cells (rods and cones)Rod cell functions in less intense lightCone cell functions in bright light.

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Optic NerveThe optic nerve transmits electrical impulses from the retina to the brain.  It connects to the back of the eye near the macula. 

The optic nerve is a bundle of more than 1 million nerve endings. It connects the retina to the brain

TEAR

Tears are secretions of various gland that clean and lubricate the eyes.

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Types of TearSome of the different types of tears the brain tells the eyes to produce are: 1.Basal tears that coat your eyes on a day-to-day basis to keep them moisturized.2.Irritant/reflex tears that form in response to pain or to flush foreign objects out of the eye. Their composition is similar to basal tears, but they contain more healing properties.3.Emotional tears that appear in response to feelings of sadness, stress, joy and extreme emotion.

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Flow of tears

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Layers of tear filmComposed of three layers 1.Outermost lipid layer: secreted by meibomian glands. 2.Middle aqueous layer: Secreted by lacrimal gland 3.Innermost mucin layer: Produced by the conjunctival goblet cells

Human Eye

Pupil} Conjunctiva

CorneaLens

Iris

Suspensory Ligaments

Ciliary Body

Lacrimal Gland

RetinaChoroidSclera

Canal of SchlemmVitreous Humour

Aqueous HumourFovea

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Optic Disc

Human Eye

Pupil} CorneaIris

Sclera

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